Each of these applications is hereby incorporated by reference as if fully set forth herein.
1. Field of the Invention
The invention relates to television signals.
2. Related Art
Television transmitters and receivers use a known standard encoding for signals describing the television picture to be broadcast and displayed. Known television signal encoding includes standards known as NTSC (used in the United States), SECAM (used in France), and PAL (used in Germany). Each of these television signal standards represents the television picture using three components: Y (luminance), I and Q (the two components of chrominance). These television signals are referred to as being in YIQ format (or in YUV format, which is similar).
One problem in the known art is that there is difficulty in displaying foreground text in color against a background color or another underlying image (such as a dynamic image as in broadcast television). Depending on the choice of foreground color, the text can be difficult to read, can present substantial flicker (even for static pictures), and can present visual artifacts at borders of color changes in the background. Many artifacts are themselves introduced by attempts by television receivers to separate the Y component from the I and Q components when they have been combined into a single composite video signal.
Accordingly, it would be desirable to provide an improved method and system for presenting color television signals. This advantage is achieved in an embodiment of the invention in which television signal luminance and chrominance values for foreground elements are adjusted in response to television signal chrominance values for background elements, so as to minimize display artifacts while preserving the relative visual contrast between foreground and background.
The invention provides an improved method and system for presenting color television signals. Television signal luminance and chrominance values for foreground elements are adjusted in response to television signal chrominance values for background elements, so as to minimize display artifacts while preserving the relative color contrast between foreground and background.
The invention modifies chrominance values of the foreground color to reduce the difference of the foreground chrominance by a scaling factor with respect to the background chrominance, and the luminance value of the foreground color by the same scaling factor to maintain intended visual contrast between foreground and background colors. In this manner, through appropriate choices of scaling factors, the invention modifies the luminance and chrominance values of the foreground color to avoid color combinations known to display poorly for selected output devices.
An embodiment of the invention modifies the luminance and chrominance values of the foreground color to decrease cross-luminance separation artifacts at the border between foreground and background colors.